Hydraulic lift systems of the forgoing type for driving downhole pumps in well applications are known in the art, and include those disclosed in US2012/0148418, US2014/0234122, US2014/0079560, US2015/0176573, US2015/0285243, U.S. Pat. Nos. 7,562,701, 8,083,499, and 8,562,308.
Among these references, U.S. Pat. No. 8,083,499 discloses offsetting of the piston rod from the central longitudinal axis of the cylinder in order to resist rotation of the piston relative to the cylinder, thereby preventing damage to a position sensor probe along which the piston is slidable. In this reference, the piston rod extends vertically upward from the hydraulic linear actuator and is indirectly coupled to the pump rod via a cable routed over a sheave that is carried atop the piston rod.
U.S. Pat. No. 7,562,701 also discloses prevention of piston rotation relative to the cylinder in a hydraulic lift apparatus by offsetting of components relative to the central longitudinal axis of the cylinder, but does so for the purpose of enabling rotational manipulation of downhole equipment. The hydraulic linear actuator is installed within an uppermost portion of the wellhead casing rather than atop the wellhead, and so hydraulic supply lines enter the upper end of the cylinder and are routed downwardly through the piston in order to pressurize the cylinder below the piston to drive the upstroke, and a hollow ram accommodates passage of the well fluid to the surface. The ram and fluid supply lines are offset from the central longitudinal axis of the cylinder to prevent rotation of the piston.
US20140234122, US20120148418 and US20150176573 disclose hydraulic lift systems that, like U.S. Pat. No. 8,083,499, employ a magnetorestrictive probe to monitor the position of the sliding piston, but place this probe externally of the cylinder and have the piston rod extending downwardly from the cylinder for inline connection to the pump rod.
Disclosures concerning piston rotation prevention and piston position detection in the general area of piston cylinder assemblies used in other applications be found in JP2005054977 and U.S. Pat. No. 7,493,995.
Applicant has developed a new hydraulic lift design incorporating unique features neither shown or suggested by the prior art